Linear motion guide units conventionally incorporated in diverse machinery are ordinarily fed with lubricant every a preselected interval based on maintenance schedules to make certain of forming the lubricant film separating a rolling element from a load-carrying race, ensuring sustainable smooth rolling motion of the rolling element throughout a circulating circuit. Meanwhile, modern advanced machines and instruments are increasingly needed to work virtually in maintenance-free operating conditions from many aspects of conserving energy as well as keeping running cost and maintenance cost of equipment reasonable. Correspondingly, the linear motion guide units used in the advanced machinery are also challenged to keep the consumption of lubricant to a minimum, along with keeping linear motion guide units virtually maintenance free for lubrication over long-lasting operation.
The linear motion guide units of the class using cylindrical rollers as the rolling elements have been especially needed to work with maintenance free conditions for lubrication. Most conventional linear motion guide units are composed of an elongated guide rail and a slider that moves relatively to the guide rail by virtue of more than one rolling element, which is allowed to roll through a circulating circuit that is made up of a load-carrying race defined between the guide rail and the slider, and a non-loaded area including a return passage and forward and aft turnaround passages made in the slider. With the linear motion guide units constructed as stated earlier, continuous application of lubricant on or between the load-carrying race and the rolling element is inevitable to continue maintaining an adequate lubricant film between the load-carrying race and the rolling element to keep them against metal-to-metal contact that might otherwise occur, thereby making sure of their high durability.
In the commonly assigned Japanese Patent Laid-Open No. H09-72335, there is discloses a linear motion guide unit in which a tubular member, or a sleeve, fits into a fore-and-aft hole bored in a carriage of the slider to provide the return passage. The sleeve is made easier to experience elastic deformation to absorb the frictional resistance occurring on the rolling elements, thereby ensuring smooth running of the rolling elements. With the linear motion guide unit constructed as recited just earlier, cylindrical rollers are selected as the rolling elements while the return passage is defined by the sleeve that fits closely into the return hole cut in the carriage. The sleeve is made it possible to get elastic deformation, ensuring smooth traveling of the slider. Especially, an ample circular clearance is left between the wall surface inside the return passage and the outside surface around the middle area of the sleeve to allow the sleeve to get elastically deformed therein and also reserve lubricant therein.
In another commonly assigned Japanese Patent Laid-Open No. 2001-82469, there is disclosed a linear motion guide unit in which a return passage in a carriage of the slider is made of sintered resinous member of cellular or porous structure that is impregnated with lubricant to be applied on the rolling elements. The return passage is constituted with a sleeve of sintered resinous member having porous or cellular structure, which fits into a fore-and-aft hole made in the carriage of the slider. Oily lubricant or grease once soaked in the sintered resinous member preparatory to fit into the carriage is reserved or retained in the cells or pores in the cellular structure. The rolling elements are constantly applied with oily ingredient of the lubricant while rolling through inside the sleeve, and oil films around any rolling elements get lubricating smoothly the load-carrying surfaces or raceway grooves as the rolling elements run through load-carrying race, with accompanying reduced maintenance.
Another sort of conventional linear motion guide means is disclosed in Japanese Patent Laid-Open No. H10-78032, in which there is used lubricant-containing polymer to lubricate the rolling element of ball. With the prior linear motion guide means recited now, a tubular member allowing the rolling elements running through there is made of tubular composition of lubricant-containing polymer, which is composed of cylindrical skeleton cage of polyethylene high in stiffness or mechanical strength, the skeleton cage being made therein with lengthwise windows opened from the outside to the inside thereof and spaced away circularly from one another at regular intervals around the circular surface of the skeleton cage, and lubricant-containing polymer segments that fit closely into the windows, one to each window. For production of the tubular composition of lubricant-containing polymer, the polyethylene skeleton cage prepared in advance by injection molding is positioned within a preselected mold held in any injection molding machine, and then molten lubricant-containing polymer is poured into the mold cavity, where it solidifies as it cooled, coming into joining integrally with the skeleton cage.
Another Japanese Patent Laid-Open No. 2001-248637 discloses a linear motion guide unit making it easier to ensure lubrication of circulating balls with lubricant that may be simply replenished from the outside of the guide unit, making certain of serving steadier functions in the long run even with no troublesome maintenance work. With the linear motion guide unit stated just earlier, the return passages made in the slider are each provided with a return sleeve that is lengthwise slit and lined with a lubricant applicator over the inside circular surface thereof. The fore-and-aft slit made in the return sleeve constitutes a groove that helps the lubricant spread easier lengthwise from the lubricant applicator covering the fore-and-aft slit.
With the linear motion guide unit in which rollers are selected as the rolling elements, meanwhile, alignment problems to guide rollers in good rolling order without leaning in rolling posture are more encountered, compared with the construction using balls. Besides, the rollers have to be guided not only on their circular surfaces, but also on their axially opposite end surfaces. Conventionally, there is no linear motion guide unit constructed to meet with an aspect of allowing the rollers to roll through the circulating circuit over a long-lasting service life with adequate application of lubricant, making certain of steady reliability of the maintenance-free on lubricant application.
The linear motion guide unit constructed as stated earlier in the first citation, although thought to reserve some amount of lubricant in the circular clearance, would not mean the realistic construction enough to continue feeding the rollers with lubricant, keeping the maintenance-free operation more sustainable and steadier.
With the prior linear motion guide units stated earlier in the second citation, moreover, the return passage made in the carriage of the slider is defined by just sintered resinous member of cellular geometry, which is lack of mechanical stiffness enough to make sure of steady guidance of the cylindrical rollers throughout the circulating circuit. There, advanced technology has come to hope any linear motion guide unit in which the sleeve to define the return passage in the carriage of the slider is much raised in mechanical stiffness, even with simple in construction and easier to fit it into the slider as well as making sure of positive lubricant application to the rolling elements to render the maintenance-free operation more sustainable.
With the prior linear motion guide means recited earlier in which there is used lubricant-containing polymer sleeve to lubricate the rolling element of ball, it is needed to uniformly mix polymer with oily lubricant to prepare the lubricant-containing polymer and, moreover, the lubricant-containing polymer sleeve have to be molded integrally with the skeleton cage of a preselected material high in stiffness. Production of the lubricant-containing sleeve has thus required special equipment and complicated process.
Another commonly assigned Japanese Patent Laid-Open No. 2006-105310 discloses a linear motion guide unit in which a tubular member for the return passage is constituted with a tubular composition made up of a tubular skeleton having windows and porous or cellular members that fit into the windows in the tubular skeleton. With the linear motion guide unit constructed as stated just earlier, the porous members make close fit-engagement over their inside surfaces with their mating outside surfaces of flexible spines in the tubular skeleton. Thus, the porous members could not rid themselves of mechanical deformation when the flexible spines of the tubular skeleton experienced any distortion. Such deformation that might occur in the porous members was undesired in aspects of keeping the circulation of the rollers smoother as well as the positive maintenance-free operation more sustainable.
There, it remains a major challenge to further develop the tubular composition for the turn passage in the slider so as to provide the linear motion guide unit improved in the application of lubricant around the rolling elements as well as smooth guidance of the rolling elements in the return passage.